May 3, 2018

8th Light Review

Vocab

  • Transmittance:the ability of light to pass through a medium
  • Reflection:the bouncing of light off an object
  • Absorbance:to take light in and not transmit or reflect it
  • Refraction:the bending of light waves as they travel from one medium to another
  • Angle of incidence:the angle at which light hits a substance
  • Angle of reflection:the angle at which light is reflected off a substance
  • Law of Reflection:the angle of incidence equals the angle of reflection
  • The angle at which light hits an object equals the angle at which light is reflected from that object
  • Transparent:allows the transmittance ofalmost all light, ex. a window
  • Translucent: allows the transmittance of some light, ex. frosted glass
  • Semitransparent
  • Opaque:prevents the transmittance of light, ex. an oak door
  • Color filter: absorbs all light except for a select few wavelengths
  • A red color filter absorbs all color wavelengths except for red

Light is composed of small moving particles called “photons”

-Photons move, so light is a form of kinetic energy

-Light travels as a wave

All the color we perceive is reflected light!

-We are seeing specific color wavelengths reflected into our eyes

As absorbance increases, transmittance decreases

-As more light is absorbed by a substance, less light passes through that substance

Electromagnetic spectrum: the entire range of wavelengths or frequencies of electromagnetic radiation,

ranging from gamma rays to radio waves

-Visible light is on the electromagnetic spectrum, and ranges from 400-700 nm

-As wavelength increases, energy decreases

  • Ex. gamma rays have the shortest wavelength and the highest amount of energy

-Wavelength is measured in meters

White light – composed of all wavelengths of visible light

-White objects reflect almost all light

-Prisms separate white light into all other colors

Black – absorbs almost all light

-We see the color black when very little light is reflected

-As light is absorbed by a black object, light energy is also absorbed

  • This energy is transferred to the black object, causing molecules in the object to move and vibrate this creates HEAT!!

Mirrors

-Plane: flat mirror

-Concave: the mirror bends inward

  • The mirror “caves” in
  • This makes an image bigger, ex. a dentist mirror

-Convex: the mirror bends outward

  • This makes an image smaller, ex. a road mirror

Sunset and sunrise

-Earth’s atmosphere absorbs blue and green wavelengths better than red and orange

-At sunrise and sunset, light travels through more of our atmosphere, so most blue and green wavelengths are absorbed

-Only the red and orange wavelengths can get through the atmosphere, so we see red and orange at sunrise and sunset

Nuclear fusion: when 4 hydrogen atoms come together with such force that their nuclei fuse

-The sun is our closest star

  • Earth is about 8 light-minutes from the sun
  • The sun’s core temperature is 27,000,000º F
  • The sun is composed of 75% hydrogen and 25% helium

-Where does (most) of our light come from? NUCLEAR FUSION!

  • This only occurs near the center of a star, where temperature and pressure are very high

-4 hydrogen atoms combine to create 1 helium atom and release energy in the form of a photon

-In a nuclear fusion reaction, mass is converted into energy

  • Stars convert matter into energy!!!
  • Energy is released as light in the form of a photon

-The sun converts approximately 9 billion pounds of matter into energy every second

  • The sun is our only source of energy for life on Earth!

The relationship between energy, mass, and light is represented as E = mc2

-E = energy

-M = mass

-C = speed of light

How does a prism work?

-White light contains a mixture of all wavelengths of visible light

-Different wavelengths of light are refracted to a different extent by the same medium

Focus Questions

What is the relationship between the absorption and transmission of light through transparent substances?

  • There is an inverse relationship between the amount of light that is transmitted versus the amount of light that is absorbed when light interacts with a transparent liquid.
  • As absorption increases, transmittance decreases

How does light wave interact with objects that reflect light?

  • When a light wave interacts with an object that reflects light, the angle at which the wave is reflected off the object (the angle of reflection) is equal to the angle at which it encounters the object (the angle of incidence).

How does wavelength affect the perception of light?

  • We perceive an object or medium as being a certain colorbecause those wavelengths are the ones reflected into our eyes.
  • For example, we see a lemon as yellow because yellow wavelengths are being reflected by the lemon

How does a change in mediums affect the wavelength of light?

  • When light passes from one medium to another, the speed of the wavelengths changes. This causes the light wave to change directions (the light is bent). This process is called refraction.